Generally speaking, the electrical laminate is prepared by the following methods:
Printed wirings are formed on a laminate;
(i) a method comprising a step of forming printed wirings on a substrate, a step of forming ultraviolet rays-sensitive resin layers on the both sides of the substrate and a step or irradiating ultraviolet rays to the sensitive resin layers from the both sides to form a desired pattern, or
(ii) a method comprising a step of forming ultraviolet rays-sensitive resin layers on the both sides of a substrate, a step of forming a desired pattern by means of ultraviolet rays and a step of forming electroless plating layers on the pattern to form printed wirings.
In these methods, ultraviolet rays are necessarily irradiated onto the sensitive resin layers from the both sides at the same time. In this case, there is a possibility that the ultraviolet rays pass through the laminate and sensitize the sensitive layer of the opposite side. This inhibits the forming of a precise pattern.
In the prior art, laminates or metal foil-clad laminates have been prepared by laminate-molding prepregs obtained by impregnating glass non-woven fabrics or glass woven fabrics with epoxy resin and drying them, or by stacking the prepreg and a metal foil and then laminate-molding them, respectively. In such prior art, in order to prevent passing of ultraviolet rays through the laminate, an inorganic filler or a dyestuff has been incorporated into the resin component in the laminate. After the resin containing an inorganic filler or a dyestuff was cured, that the inorganic filler or the dyestuff sometimes discolored the cured resin. Japanese Patent Public Disclosure (Kokai) No. 132390/1987 etc. disclose that an ultraviolet rays-absorber and/or a fluorescent brightener is incorporated into the resin in the laminate. However, the ultraviolet rays-absorber does not completely absorb the light having 300-420 nm under which a conventional resist is sensitized, and discolors the resin. The fluorescent brightener generates fluorescence.